Genetic diversity assessment and selection of Bradyrhizobium strains for Inceptisols based on symbiotic performance

Abstract

The symbiotic association of pigeonpea (Cajanus cajan (L.) Millsp.) with rhizobia plays a pivotal role in plants’ growth and development. The present study was carried out at Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh during 2018–2020 to explore the diversity of rhizobia present in the Cajanus cajan root under Inceptisols and identify an elite strain that exhibits exceptional plant growth promotion and of nitrogenase activity for efficient nitrogen fixation. The bacterial identification using 16s rDNA sequencing revealed bacteria strains Bradyrhizobium japonicum (S12), Bradyrhizobium subterraneum (S1, S7, S8, S10, S13), Bradyrhizobium yuanmingense (S2, S3, S4, S6, S9, S11) while two bacteria were the endophytes identified as Pseudomonas azotoformans (S5) and Paenibacillus seodonensis (S15). Genetic diversity using UPGMA clustering revealed remarkable genetic variations, classifying 14 strains into three primary clusters and four secondary clusters. Strains S1, S3, S6, S9, and S13 exhibited elevated nitrogenase activity, indicative of their proficient nitrogen fixation capability. In plant growth experiments, all strains demonstrated significant growth of the plants compared to control. The notable growth enhancement by these five strains can be attributed to their remarkable efficiency in nitrogen fixation, as indicated by significantly higher nodule formation and nitrogenase activity. These findings provide valuable insights for identifying potential rhizobial inoculants to enhance pigeonpea productivity.